1. Field of the Invention
This invention generally relates to a linear motion guide unit, and, in particular, to a stopper assembly for use in a linear motion guide unit, such as a linear motion rolling contact guide unit. More specifically, the present invention relates to a stopper assembly for limiting a relative motion between a slider and a rail in a linear motion guide unit.
2. Description of the Prior Art
A linear motion rolling contact guide unit is well known and it generally includes a rail extending over a desired distance, a slider slidably mounted on the rail and a plurality of rolling members interposed between the rail and the slider to thereby provide a rolling contact between the rail and the slider. Typically, the rail has a pair of opposite side surfaces, each of which is formed with an inner guide groove extending in parallel with the longitudinal axis of the rail. The slider, typically, has a generally U-shaped cross section and thus a horizontal section located above the rail and a pair of vertical sections extending vertically downward from the horizontal section. Each of the vertical section is formed with an outer guide groove located opposite to a corresponding one of the inner guide grooves of the rail so that a guide channel is defined between a pair of oppositely located inner and guide grooves. And, a plurality of rolling members, such as rollers or balls, are provided in the guide channel so as to provide a rolling contact between the rail and the slider.
Such a linear motion guide unit can be either of the infinite stroke type or of the finite stroke type. In the former case, at least an endless circulating path is provided in the slider, and the endless circulating path typically includes a load path section, which corresponds to the above-mentioned guide channel, a return path section and a pair of curved connecting path sections, each connecting the corresponding ends of the load and return path sections. With this structure, theoretically speaking, since the rolling members can roll along the endless circulating path indefinitely, the slider could move along the rail as long as the rail extends. On the other hand, in the case of the finite stroke type, no such endless circulating path is provided and thus the relative motion between the rail and the slider is limited according to their sizes.
In such a linear motion guide unit, since the slider move along the rail, a stopper assembly must be provided to limit the relative motion between the slider and the rail. Otherwise, the slider may slip away from one end of the rail. In addition, when such a linear motion guide unit is shipped, transported or handled for some reason, such as mounting on an object, it is often desired to have such a stopper assembly to prevent the relative motion between the slider and the rail temporarily.
Several stopper assemblies for use in such a linear motion guide unit have been proposed as described in the Japanese Pat. Post-exam Pub. No. 62-8432 and the Japanese Pat. Laid-open Pub. No. 2-300517. However, in the case of a stopper assembly disclosed in the above-mentioned Pub. No. 62-8432, the stopper assembly includes a downwardly extending projection and thus a detent hole must be provided at the top surface of the rail. As a result, an extra step for providing such a detent hole is required and there is no freedom in selecting the location of the rail on which such a stopper assembly is to be mounted.
On the other hand, a stopper assembly described in the other Pub. No. 2-300517 is illustrated here in FIG. 4. As shown in FIG. 4, the stopper assembly generally includes a generally C-shaped main body E provided with a threaded hole B and a bolt A threaded into the hole B. As the bolt B is turned to further extend through the hole B, a central portion of the main body where the hole B is provided is lifted upward and away from the top surface D of a rail C so that moments M1 and M2 are applied to both ends of the main body E. As a result, clamping forces P1 and P2 directed opposite to each other are applied at contact points H1 and H2 between the bottom ends of hook portions F1 and F2 and guide grooves G1 and G2 of the rail C.
When the central portion of main body E where the threaded hole B is provided is lifted upward in this manner, a stress concentration occurs in that portion of main body E since the cross sectional area is rather small. For this reason, in the stopper assembly shown in the Pat. Laid-open Pub. No. 2-300517, there is a need to increase the rigidity of main body E. However, if the rigidity of main body E is increased, the probability of producing scars or damages in the surface of guide grooves F1 and F2 at contact points H1 and H2 increases. Thus, in order to cope with this situation, there arises a need to provide a lining of an elastic material, such as rubber, on the main body E, which then tends to push up the manufacturing cost.
If the rigidity of the main body E is increased, the rigidity of bolt A for lifting the central portion of the main body E also increases. However, if the rigidity of bolt A is increased, there is an increased chance that the top surface D of rail C becomes deformed or damaged as pressed by the bottom end of the bolt A when the bolt A is forcibly turned to further extend through the threaded bold B.